Light sensitive paper and sensitizing composition therefor



Patented Feb. 6, 1940 PATENT OFFICE LIGHT SENSITIVE PAPER AND SENSITIZING COMPOSITION THEREFOR Gustav A. Hinkel, Pittsburgh, Pa., assignor to B. K. Elliott Company, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing.

24 Claims.

' My invention relates to the art of preparing light'se'nsitive papers, cloth and other suitable Qmaterials, hereinafter referred to generally as paper and 'in their sensitized form as "blue print paper, for use in making reproductions, especially of p ans and line work by superimposing upon, the blue print paper a drawing, tracing or the like made on transparent or translu- "cent material, exposing it to the light and then developing it by-means of successive treatments withwater and an oxidizing agent.

The principal object of my invention is the provision of a sensitized composition for the production of an improved blue print paper of exceedingly fine keeping qualities, unusually high printing speed and minimized tendency to curl.

Prints made from my improved paper .show great contrasts due to very dark blue back grounds and decidedly'pure white details. Furthermore these prints are extremely resistant to the bleaching effect of the light rendering them practically fade proof.

As is known to those skilled in the art, blue print papers are commonly prepared by coating 9. suitable paper with a sensitizing composition consisting of an aqueous solution of ferric alkali 7 metal salts of organic acids, such as ferric amnide, and its subsequent interaction with the ferric ammonium oxalate simultaneously present in the light sensitive layer, a blue compound commonly termed Prussian bluefis formed prior to exposure to the light. This compound will be referred to hereinafter as Prussian blue irrespective of the scientific correctness of its name or the theory of its formation.

This Prussian blue is insoluble in the water which is used for washing the prints in the process of their development, causing the lines and other details of the blue prints to assume a blueish tinted appearance. Since this tinting materiallydecreases the contrasts in these prints, blue print papers coated with that type of sensitizing composition are unsatisfactory.

Satisfactory results as to producing white details are known to be obtainable by the addition of an acid, such as phosphoric acid or oxalic acid, or an acid alkali metal salt such as sodium binoxalate or ammonium dihydrogen phosphate, or a'kaline hydrolizing alkali metal salts such as sodium oxalate or potassium monohydrogen phosphate, to the sensitizing compositions comprising an aqueous solution of, for example, ferric ammonium oxalate and potassium ferricya- Application February 20, 1939; Serial No. 257,331

soluble compound more or less white lines or details are characteristic of prints made from paper coated with a sensitizing composition containing a certain amount of aforementioned acids, acid salts or alkaline hydrolyzing salts, besides ferric a kali metal salts of organic acids and alkali metal ferricyanides. Despite the obvious advantage of improved contrasts and undisputed superior keeping qualities of these blue print papers they, neverthelesalack a satisfactory printing speed.

More recently and as disclosed in British Patent No. 418,369 to J. Halden 8: Company, Limited, and United States Patent No. 2,093,738 to Alger P. Reynolds, alkali metal ferrocyanides, such as potassium ferrocyanide, sodium ferrocyanide or ammonium ferrocyanide, are used as the full or partial substitute for alkali metal ferricyanides,

such as potassium ferricyanide, sodium ferricyanide orammonium ferricyanide contained in heretofore employed blue print paper sensitizing solutions. The purpose of this is to eliminate or minimize the obviously light screening action of the traditionally used strongly yellow colored alkali metal ferricyanides.

Under ordinary circumstances the presence of alkali metal ferricyanides in blue print paper sensitizing solutions containing organo alkali metal ferric salts, such as ferric ammonium oxalate, and alkali metal ferricyanides such as potassium ferricyanide, would as stated supra cause the formation of Prussian blue, and paper coated with such a solution would be unsatisfactory, despite its faster printing speed, due to the fact that blue prints made from this paper show strongly blue colored lines instead of contrasting white lines on a blue background. Therefore the presence of Prussian blue, even though finely suspended, renders the composition unsuitable as a sensitizing solution for blue print paper? Both the above mentioned patents call for the" addition to this sensitizing solution of certain ingredients to prevent the formation of Prussian blue. These are referred to as alkaline buffer salts of alkali metals or alkaline hydrolyzable alkali metal compounds. According to both patent disclosures the ingredients used to make up this type of blue print sensitizing solution, which hereafter will be referred to as ferrocyanide blue print solution, are similar if not identical and so arethe solutions, with the exception of the final acidity or more correctly the-value of the hydrogen ion concentration or, in other words, the pH value of both types of solution; Holdens ferrocyanide blue print solution being neutral or slightly alkaline claiming a pH value of '7 or higher while Reynolds solution is acid claiming a pH value of lower than '7.

I discovered a new and useful method of preventing the formation of Prussian blue in ferrocyanide blue print solutions by means of incorporating into such compositions salts consisting of a dibasic or tribasic acid either organic or inorganic and a hydroxyalkyl amine either a primary, secondary or tertiary amine irrespective of the final pH value of such solutions, although I prefer a pH value of 7 or below 7 but preferably not below 3.

The particular advantage of using hydroxyalkyl amine salts lies in their comparatively great solubility in water which, for example, in the case of tri hydroxyethyl amine oxalate is unlimited. This fact and the fact that hydroxyalkyl amines readily dissolved basic ferrous salts of organic acids, assumed by the art to be presentin the background of the prints after exposure to the light, provides for speedy development into blue prints of unexcelled fastnessto light and which may be more fully explained by the following facts: T

The process of development consists mainly in washing the prints with water thereby removing all the chemicals that are not afl'ected or are only partially afiected by the actinic rays of the light thus fixing the white lines or details or the print, and removing all the chemicals which have no part in the formation of the blue background of the print, especially the abovementioned basic ferrous salts of organic acids. The, process further comprises the oxidation of the originally light colored background into a deep lue. It is to be noted that the incomplete removal of the basic ferrous salts results in their subsequent oxidation into light sensitive ferric salt and this in turn is the reason for bleaching when those prints are exposed to the light.

Another advantage of using hydroxyalkyl amine salts and particularly tri hydroxyethyl amine oxalate lies in their slight hygroscopicity which is less than for instance that oi glycerin but high enough to act as a humidifying agent for the paper, thus producing in the sensitized material a higher grade of suppleness. This action on the paper is facilitated owing to the fact that a number of hydroxyalkyl amine salts, such as di hydroxyethyl amine oxalate, tri hydroxyethyl amine phosphate, tri hydroxyisopropyl amine oxalate, and others known to those skilled in the art, are at commonly prevailing temperatures of a viscous oily consistency, instead of being solid crystals as is the case with alkali metal salts. This improved suppleness is especially desirable in sheetprinting where stiii. sheets of blue print paper having a tendency to curl and to roll up retard production.

Among the salts capable of preventing the formation of undesirable Prussian blue in ferrocyanide blue print solutions and falling within the scope of this invention, without limiting myself thereto, are the following: mono hydroxymethyl amine oxalate, mono hydroxyethyl amine phosphate, mono .hydroxyethyl amine citrate, mono hydroxypropyl amine tartrate, mono hydroxyisopropyl amine oxalate, di hydroxyisopropyl amine oxalate, d1 hydroxyethyl amine oxalate, di hydroxyisobutyl amine phosphate, tri hydroiwethyl amine tartrate, tri hydroxyethyl amine oxalate, tri hydroxymethyl amine phosphate, tri hydroxypropyl amine tartrate, tri hydroxyisopropyl amine borocitrate, tri hydroxybutyl amine glycerophosphate and others known to those skilled in the art.

Within the scope of the discovery are complex salts consisting of a residue of a suitable dibasic acid and a suitable metal of the first or second group of the periodical arrangement of the element not forming water insoluble compounds with ferrocyan'ide or ferricyanide ions and either primary, secondary or tertiary hydroxyalkyl amines. By suitable dibasic acid I mean such acids as tartaric acid, oxalic acid, malic acid and others known to the ones skilled in the art.

By a suitable metal of the first or second group in the above connection, I am referring to such metals as sodium, potassium, ammonium which although not strictly a metal is generally classed here, magnesium, calcium and others known to the onesskilled in the art. Complex salts of the type which I am referring to -are such as tri hydroxyethyl amine potassium oxalate, di hydroxyisopropyl amine sodium tartrate, tri hydroxymethyl amine ammonium malate and others known to those skilled in the art.'

I also include complex salts consisting of a suitable tribasic acid such as phosphoric acid, citric acid, boric acid, and one or two suitable metals of the first or second group of the periodical arrangement of the elements which do notform water insoluble compounds with ferrocyanide or ferricyanide ions which are referred to in the preced-- ing paragraph, and one or two, as the case may be. of the mono, di, or tri hydroxyalkyl amines, particularly salts such as mono di hydroxyethyl amine sodium hydrogen phosphate, mono tri hydroxyisopropyl sodium magnesium citrate, mono hydroxymethyl potassium glycerophosphate and similar salts known to those skilled in the art.

I furthermore include complex salts of a dior tribasic acid, such as mentioned above, and two or three, as the casemay be, difl'erent mono, di

or tri hydroxy alkyl amines. Salts inthis class are as follows: Di hydroxyethyl amine tri hydroxy methyl amine oxalate, tri hydroxyisopropyl amine trl hydroxyethyl amine hydrogen.

phosphate, mono hydroxyethyl tri hydroxyethyl tri hydroxypropyl amine citrate and other similar salts known to those skilled in the art.

. It is within the scope 01' this invention to use any such acids and bases or acid and alkaline reacting chemicals which when added to the ferrocyanide blue print solution would give rise to the formation of salts or complex salts of the aforedescribed nature.

The following examples are ferrocyanide blue print solutions typical for this invention:

. Example #1 Water ccs 1,000 Tri hydroxyethyl amine oxalate ..grams Sodium ferro-cyanide do-.. 40 Potassium ferricyanide do 10 Ferric ammonium oxalate -d,o ,150

the amount of tri hydroxyethyl amine oxalate being used as a restrainer to prevent the formation of Prussian blue can be varied and if so should be regulated in accordance with the amount of sodium ferrocyanide substituting for potassium ferricyanide. If' more hydroxyalkyl amine salt is used than is required to prevent changing the other ingredients of above formula,

the blue background will be deepened, but at the expense of the reduction of the printing speed:

Thekeeping qualities as well as the whiteness of the details are not. only retained but rather improved.

In Example #1 tri hydroxyethyl amine oxalate isbeing used as a restrainer to prevent the formation of Prussian blue. Equivalent amounts of tertiary hydroxyalkyl amine oxalates other than tri hydroxyethyl amine oxalate, can be substituted therefor, such salts as tri hydroxymethyl amine oxalate, tri hydroxyisopropyl amine oxalate, tri hydroxybutyl'amine oxalate and similar ones. Equivalent amounts of primary and secondary hydroxyalkyl amine oxalates canalso take the place of tri hydroxyethyl amine oxalate, and I name salts such as mono hydroxymethyl amine oxalate, mono hydroxyethyl amine oxalate, mono hydroxybutyl amine oxalate, di hyhydroxyethyl amine oxalate. di hydroxypropyl amine oxalate, di hydroxyisobutyl amine oxalate Example #2 Water ccs 1,000 Di .hydroxyethyl amine potassium oxalate grams Sodium ferrocyanide do 35 Potassium ferricyanide ..do.. 15 Ferric ammonium oxalate In this ierrocyanide blue print solution a complex salt is used as a restrainer to prevent formation of Prussian blue. It consists besides the oxalic acid residue of the alkali metal potassium and the secondary hydroxyalkyl amine di hydroxyethyl amine. In this formula, too, any

other suitable primary, secondary or tertiary hydroxyalkyl amine may take the place 01 above mentioned secondary amine, and any other suitable metal of the first or second group of the periodically arranged system of the elements may be substituted for potassium such as sodium, lithium, ammlonium (this latter one although not strictly a metal is generally classed here), magnesium, strontium and others known to those skilled in the art. The alkali metal potassium can furthermore be replaced by any such primary, secondary and tertiary hydroxyalkyl amines as hereinbei'ore mentioned.

Instead of the residue of oxalic acid other such acid residues as already referred to under Example #1 can form the acid constituent oi complex salts intended to be used in the formula of Example #2.

Another formula tor a suitable ierrocyanide solution is given as follows:

Example #3 Waterres-.. 1,000 Oxalic acid grams 37.8 Tri hydroxyetbyl amine do- 89.4 Sodium ferro cyanide -do- 30 Potassium ferricyanide do 20 Ferric ammonium oxalate "do"-..

This ierrocyanide blue print solution is similar as to its characteristics to the one given as Example #1. Although the two ingredients oxalic acid and tri hydroxyethyl amine are not recorded in that Iormula the similarity 01 both.

oxalate when dissolved. It isunderstood that solutions is established throuah the fact that the stoicheiometrically equivalent amounts of oxalic acidand tri hydroxyethyl amine which are used in Example #3 form tri hydroxyethyl amine skilled in the art can take its place.

It is within the scope of this invention to use various suitable acids simultaneously with either one or-any number of corresponding amounts of hydroxyalkyl amine bases to form mixtures of hydroxyalkyl amine salts.

Another formula for a suitable ierrocyanide blue print solution is given as follows:

Example #4 Water ces 1,000

Tri hydroxyisopropyl aminegrams 59.4 Potassium binoxalate"; do Sodium ferrocyanide"; do- Potassium ierricyanide do Ferric ammonium oxalate --do The ierrocyanide blue print solution made up 1 according to this formula is similar as to the characteristics of its ingredients to Example #2, inasmuch as the 'stoicheiometrically equivalent amounts oi potassium binoxalate and tri isopropyl amine form a complex salt, i. e. tri hydroxyisopropyl amine potassium oxalate when dissolved together in the required amount of water. I do not intend to limit myself to the use'oi potassium binoxalate as the only acid salt, nor to the use of tri, hydroxyisopropylamine as the only hydroxyalkyl amine base forming. complex salts used as restrainers to prevent formation of Prussian blue in ierrocyanide blue print solutions. I include any other suitable acid salts such as the binoxalates, the bitartrates, the'bimalates, the mono hydrogen phosphates and cit- 5 rates, the di hydrogen phosphates and citrates oi the metals of first and second group of the periodically arranged system of the elements including ammonium and also including any 01' the primary, secondary and tertiary hydroxyalkyl amine bases hereintotore mentioned such as the binoxalates 01' ammonium, sodium mag-- nesium, hydroxyalkyl amine bases, the bitartrates of potassium, sodium. ammonium and hydroxyalkyl amine 'bases,- the mono hydrogen phosphates of potassium, sodium, ammonium magnesium-and hydroxyalkyl-amines and many others known to those skilled in the art.

Instead of tri hydroxyisopropyl amine any The stoichelometrically equivalent amounts of oxalic acid, potassium oxalate and tri hydroxy- 75 I oxalate.

ethyl amine mentioned above form when brought in solution tri hydroxyethyl amine potassium Thus this ferrocyanide solution is in every respect similar to the solutions prepared in accordance with the formulae of Examples #2 and #4, all three solutions containing complex salts after solution has been efiected. It is unnecessary to enumerate all the possibilities as to suitable acids that can be used instead of oxalic acid neither need I' mention the various salts of di and tri basic acids to substitute for potassium oxalate orother hydroxyalkyl amines to take the place of tri hydroxyethyl amine, these being evident, to those skilled in the art, from the foregoing paragraphs.

It is understood that the amounts of ingredients in any of the referred to examples are not given with the intention of confining myself a strictly to these figures or ratios or multiples of them any one of these amounts being subject to changes. Neither do I intend to restrict the number of ingredients of my new type of ferrocyanide blue print solution to the number of ingredients recorded in those examples. I prefer for instance to add small amounts of from 1 to 5 grams of an acid such as oxalic acid, citric acid, tartaric acid, phosphoric acid to hereinreferred to formulae with the purpose of accelerating the printing speed of the paper coated with said solutions. I furthermore include additions such as saponine or sulphonated fatty acids to facilitate their absorption by particularly hard papers and catalysts such as salts of vanadic acid to increase the printing speed of this new type of blue print paper. I am aware of the fact that ferric ammonium oxalate used in all examples as the light sensitive ferric alkali metal salt is a complex salt and can be replaced by any other organo ferric salt together with alkali metal salts of di or tri basic organic acids to form complex salts when dissolved. Y

'I claim:

1. A sensitizing composition for blue print paper and the like which comprises an aqueous solutionof a ferric alkali'metal salt 01 an organic acid, an alkali metal ferrocyanide, and a hydroxyalkyl amine salt of 'a polybasic acid.

2. A sensitizing composition for blue print paper and the like which comprises an aqueous solution of a ferric alkali metal salt of an organic acid, an alkali metal ierrocyanide, an alkali metal ferricyanide, and a hydroxyalkyl amine salt of a polybaslc acid.

3. A sensitizing composition for blue print paper and the like comprising an aqueous solution in accordance with claim 1, wherein the hydroxyalkyl amine salt is tri hydroxyethyl amine oxalate.

4. A sensitizing composition for blue print paper and the like comprising an aqueous solution in accordance with claim 2, wherein the hydroxyalkyl amine salt is tri hydroxyethyl amine oxalate.

5. A sensitizing composition for blue print paper and the like which comprises an aqueous solution of a. ferric alkali metalsalt of an organic acid, an alkali metal ferrocyanide, and a complex salt of a polybasic acid with a hydroxyalkyl amine base, and a suitable metal of the first or second group of the periodically arranged s stem of the elements.

6. A sensitizing composition for blue print paper and the like which comprises an aqueous solution of a ferric alkali metal salt of an organic acid, an alkali metal ferrocyanide, an alkali metal cordancewith claim 10, wherein the hydroxvalky complex salt is tri hydroxyethyl amine potassium 1 light-sensitive coating comprising. a ferric alkali oxalate. V I .7 9. Blue print paper and the like having a metal salt of an organic acid analkali metal I ferrocyanide and a hydroxyalkyl amine salt of a polybasic acid.

10. Blue print paper and the likehaving a light-' sensitive coating comprising a ferric alkali metal salt of an organic acid, an alkali metal ferrocyanide, an alkali metal ferricyanide, and a H hydroxyalkyl amine saltof a polybasic acid.

11. Blue print paper and the like having a light-sensitive coating of the character in accordance with claim 9, wherein the hydroxyalkyl amine salt is tri hydroxyethyl oxalate.

12. Blue print paper and the like havin a I light-sensitive coating of the characterf -gm ac amine salt, is tri hydroxyethyl oxalate. 13. Blue' print paper and the like having a light-sensitive coating comprising a ferric alkali metal salt of an organic acid, an alkali metal ferrocyanide, and a complex salt of a polybasic acid with a hydroxyalkyl amine base, and a suitable metal of the first or second group of the periodically. arranged system of the elements. v

14. Blue print paper and the like having a light-sensitive coating comprising a ierric alkali metal salt of an organic acid, an alkali metal ferrocyanide, an alkali metal ferricyanide, and a complex salt of a polybasic acid with a hydroxyr alkyl base, and a suitable metal of the first or second group of the periodically arranged system 01' the elements. I

15. Blue print paper and the like having a light-sensitive coating of the character in accordance with claim 13, wherein the hydroxyalkyl amine salt is tri hydroxyethyl oxalate.

16. Blue print paper and the like having a light-sensitive coating of the character in accordance with claim .14, wherein the hydroxyalkyl amine salt is tri hydroxyethyl oxalate.

1'7. A product consisting of an adaptable base and a light-sensitive layer thereon containing a ferric alkali .metal salt of an organic acid, an alkali metal ferrocyanide, and a hydroxyalkyl amine salt of a polybasic acid. I

18. A product consisting of an adaptable baseferric alkali metal salt of an organic acid, an II 2,188,900 a I I 5 of the first orsecond group of the periodically. arranged system of the elements. v

10 a hydroxyalkyl amine base and a suitable metal 23. A product in accordance with claim 21 wherein the hydroxyalkly amine salt is tri hydroxyethyl amine oxalate. 5

24. A product in accordance with claim 22 wherein the hydroxyalkyi amine salt is tri' hydroxyethyl amine oxalate.

GUSTAV A. HINKEL. 1o 

